The present invention relates to the art of metal surface treatment. More specifically, the present invention relates to the art of post-treating a conversion coated metal surface to impart improved corrosion resistance and paint adhesion characteristics thereto.
The need for applying protective coatings to metal surfaces for improved corrosion resistance and paint adhesion characteristics is well known in the metal finishing and other metal arts. The usual technique for applying such protective coatings to metal surfaces involves contacting the metal surface with a solution containing phosphate ions to form a corrosion resistant, nonreactive phosphate complex coating on the metal surface. Such coatings convert the metal surface from a chemically active surface readily susceptible to oxidation and are known in the art as "conversion coatings."
The corrosion-resistance of conversion coatings can be enhanced by treating the phosphatized metal surface with an after-treatment solution such as a dilute aqueous acidic solution containing a hexavalent chromium compound. However, although chromium after-treatment solutions and processes are known to be effective, in recent years there has been development effort directed to discovering effective alternatives to the use of chromium-containing post-treatments for conversion coatings.
In accordance with the present invention a composition which is alternative to hexavalent chromium compound containing solutions is provided for use in a novel process for the post-treatment of phosphatized or conversion coated metal surfaces. The solution and post-treatment process of the present invention are effective to enhance the corrosion resistance and paint adhesion characteristics of a conversion coated metal surface. Further understanding of this invention will be had from the following disclosure wherein all percentages are by weight unless otherwise indicated.